1. Field of the Invention
The present invention relates to an ESD protection device, and a common mode choke coil with a built-in ESD protection device including an integral structure including an ESD protection device and a common mode choke coil in a multilayer body.
2. Description of the Related Art
ESD (electro-static discharge) is a phenomenon in which discharge occurs when an electrically-charged conductive substance (a human body, connector, or the like) makes contact with or comes close enough to another conductive substance (an electronic apparatus or the like). ESD protection devices are configured to release ESD to the ground or the like and disposed, for example, between a signal line in a circuit and the ground (earth).
To prevent damage, malfunctions, and so on of electronic apparatuses caused by ESD, a variety of ESD protection devices have been conceived as a counter measure against ESD. For example, International Publication No. WO 2008/146514 discloses an ESD protection device (spark gap type) having a configuration in which there are provided, in a hollow portion provided inside a multilayer body, a discharge electrode and a ground electrode opposing each other, and an auxiliary electrode that is disposed adjacent to the discharge and ground electrodes opposing each other.
Meanwhile, to suppress common mode noise that propagates in differential transmission lines, common mode choke coils have been generally used as common mode filters, and a variety of common mode choke coils with a built-in ESD protection device of the spark gap type have been conceived as a countermeasure against ESD. For example, in each of International Publication No. WO 2013/136936 and International Publication No. WO 2013/99540, there is disclosed a lamination-type common mode choke coil of an array type having a structure in which two hollow portions are arranged on the right and left sides when viewed in a lamination direction, and ESD protection devices are separately formed in each of the hollow portions.
In the case where a multilayer body having a structure in which ESD protection devices are separately formed in each hollow portion is miniaturized, there arises a problem such that a plurality of hollow portions are disposed nearby each other and consequently the hollow portions are connected to each other. Because of this, in the structure where the hollow portions are individually provided for each ESD protection device, a certain amount of occupation space needs to be secured, which makes it difficult to realize the miniaturization. Accordingly, in order to miniaturize an electronic component including a plurality of ESD protection devices inside a multilayer body, it is essential to use a structure in which a ground electrode and a plurality of discharge electrodes are disposed in a single hollow portion.
However, in the case where the above structure is used, when static electricity enters a transmission line, in addition to the occurrence of discharge between the discharge electrode and the ground electrode, abnormal discharge among the plurality of discharge electrodes is likely to occur because the plurality of discharge electrodes are arranged adjacent to each other in the shared hollow portion. In the case where the discharge among the discharge electrodes (hereinafter, referred to as “abnormal discharge”) occurs, the static electricity having entered one transmission line moves to another transmission line, which raises a risk of breakdown of an electronic circuit such as an IC or the like that is connected to a subsequent stage of a common mode choke coil.